This invention relates to providing a bag of heat-sealable construction which comprises at least one ply of an opaque barrier sheet peelable from the remaining structure, preferably to allow viewing of the contents of the bag. The bag is characterized by good strength and the fact that it can be thermally sterilized without substantially interfering with the heat-seal.
Window-type constructions on plastic packages are known in the prior art. For example, such constructions are disclosed in German Offenlegungsschrisft 25 39 351. A somewhat similar construction is shown in U.S. Pat. No. 4,015,771.
It has remained a problem to provide a thermally-sterilized bag with a peelable window construction that is desirably strong. In some instances it may be desirable for such a bag to withstand a six-foot drop to a floor while containing a liter of liquid. To provide such a bag while, at the same time, providing a peelable, window-revealing member in the construction is a problem to which the invention is directed.